A survey of reproductive parameters in the free-ranging chimpanzees of Gombe National Park.

Abstract

This study is a review of reproductive records for chimpanzees (Pan troglodytes schweinfurthii) living in Gombe National Park, Tanzania, between 1964 and 1994. Females exhibited their first full anogenital swelling at approximately 10.8 years of age. Duration of adolescent infertility averaged 2.37 years, with first conception occurring at 12.7 years and first parturition at 13.3 years. The menstrual cycles of young nulliparous females were significantly longer than those of older multiparous females (average 39.8 days versus 33.8 days). Analysis of anogenital swelling patterns indicated an average duration of 12-13 days for maximal swelling in all classes of cycle. Nulliparous and postpartum females exhibited a similar pattern of shortened detumescent phase, indicative of anovulation. Duration of gestation averaged 225.3 days (range = 208-235) with no significant fetal gender effect. When an infant lived to weaning age, the postpartum amenorrhoea of the mother averaged 3.86 years, whereas if the offspring died as an infant the mother resumed menstrual cycles an average of 35 days later. Once postpartum cycles resumed, the next conception averaged 142.5 days later if the previous infant had survived, but sooner (92.9 days later) if the previous offspring died in infancy. Interbirth interval averaged 5.15 years. Analysis of behavioural records indicated that a lower percentage of conceptions occurred during consort matings than was previously thought, suggesting additional research is needed on this topic. Detailed discussion focuses on the environmental influence on reproductive parameters described here. Future work in this area will probably identify the importance of diet-via basic nutrition and phytochemical content-in effecting the seasonal and individual differences seen in this study.